Document and Entity Information	9 Months Ended
	Sep. 30, 2012	Oct. 30, 2012
Entity Information
Document Type	10-Q
Amendment Flag	true
Amendment Description	This Amendment No. 1 to our Quarterly Report on Form 10-Q for the quarter ended September 30, 2012, previously filed with the Securities and Exchange Commission (the Commission) on November 7, 2012, is being filed for the sole purpose of correcting the ending totals on the Consolidated Condensed Statements of Comprehensive Income. In connection with generation of the XBRL document for filing with the Commission, typographical errors resulted in incorrect Comprehensive Income or Loss totals for the three months ended September 30, 2012 and 2011 and for the nine months ended September 30, 2012. These totals have been corrected in this filing. Except as described above, no other changes have been made to the original filing and this Form 10-Q/A does not amend any other items or disclosures in the original filing.
Document Period End Date	Sep. 30, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q3
Entity Registrant Name	ENERGEN CORP
Entity Central Index Key	0000277595
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		72,146,547
Alabama Gas Corporation
Entity Information
Document Type	10-Q
Amendment Flag	true
Amendment Description	This Amendment No. 1 to our Quarterly Report on Form 10-Q for the quarter ended September 30, 2012, previously filed with the Securities and Exchange Commission (the Commission) on November 7, 2012, is being filed for the sole purpose of correcting the ending totals on the Consolidated Condensed Statements of Comprehensive Income. In connection with generation of the XBRL document for filing with the Commission, typographical errors resulted in incorrect Comprehensive Income or Loss totals for the three months ended September 30, 2012 and 2011 and for the nine months ended September 30, 2012. These totals have been corrected in this filing. Except as described above, no other changes have been made to the original filing and this Form 10-Q/A does not amend any other items or disclosures in the original filing.
Document Period End Date	Sep. 30, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q3
Entity Registrant Name	ALABAMA GAS CORP
Entity Central Index Key	0000003146
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		1,972,052